UI freezes temporarily for repos with many branches

What steps will reproduce the problem?

1. Clone a Git repo that has 3,000 active branches
2. Click the TortoiseGit "Browse References" menu command
3. Click on "remotes" -> "origin"

What is the expected output? What do you see instead?

Expected: Some branch names should appear immediately. Additional branches should load in the background, without blocking UI operations.

Actual: It takes about 5 seconds for the listview to update at all. During this time, UI interaction is frozen, and the status label "Showing 2619 ref(s), 0 ref(s) selected" as the number counts upwards and repaints after each increment. For example, clicking on "remotes" or another origin has no effect, because the UI is stuck in a repainting loop.

What version of TortoiseGit and Git are you using? On what operating system?

2.8.0.0

Please provide any additional information below.

This seems like it should be fairly easy to fix, by preventing the UI from being blocked behind the loop that is enumerating refs.